The quantum dot is a novel fluorescent platform that has the potential to become an alternative to conventional organic dyes used to label biological probes such as antibodies or ligands. Compared to typical fluorescent organic dyes, cadmium selenide/zinc sulfide core-shell nanocrystals, or quantum dots, have greater photostability, resist metabolic and chemical degradation, are nontoxic, and display broad emission and narrow excitation bands. When conjugated to generic adaptor molecules such as streptavidin, quantum dots can be used to label different biotinylated antibodies or ligands without having to customize the quantum dot surface chemistry for each antibody or ligand. In this chapter, we outline the methodology for using streptavidin quantum dots to label biotinylated antibodies that target cell-surface ectodomain proteins on both living and fixed cells.